Implantable heart stimulator

ABSTRACT

An implantable heart stimulator, comprises a pulse generator for delivering electric stimulation pulses to a patient&#39;s heart ( 21 ) through a lead ( 14 ) connectable to said pulse generator, possibly through a connector top ( 12 ) on a of pulse generator housing ( 10 ). The pulse generator housing is electrically conductive. IN an infection control apparatus for such a heart stimulator the exterior surfaces of the possible connector top and of a proximal part ( 16 ) of the lead are electrically conductive. The proximal lead part extends to a position, which after implantation of the lead is situated between a location beyond the entry to the venous system and the entry into vena cava superior. The generator housing and the electrically conductive surfaces of the proximal lead part and of the possible connector top are adapted to form a first electrode and at least one second counter electrode ( 19 ) is adapted to be loacted outside subcutaneous pulse generator pocket in which the pulse generator is located after implantation. A curent source is provided to supply an electric infection control current between the electrodes.

TECHNICAL FIELD

[0001] The present invention relates to an infection control apparatusfor an implantable heart stimulator comprising a pulse generator fordelivering electric stimulation pulses to a patient's heart through alead connectable to said pulse generator, possibly through a connectortop on a pulse generator housing, said pulse generator housing beingelectrically conductive.

BACKGROUND

[0002] Implantable heart stimulator pocket infection is a severecomplication which often ends up in explantation of the stimulator. Thereason therefor is that conventional treatment with antibiotics cannoteradicate the infection. This seems to depend on the circumstance thatthe bacteria live in a biofilm formed around the exterior surfaces ofthe implanted stimulator, which film blocks antibiotics. The bacteriamay also live passively on a very low metabolism and can therefore notbe treated successfully by antibiotics.

[0003] A method of enhancing the effect of antibiotics by applying anelectrical field across the biofilm is described in U.S. Pat. No.5,312,813. This method is based on findings by J. W. Costerton et.al.Their studies have shown that the infection can be completely cured andno explantation has to take place by applying an electric field or asmall current across the biofilm during antibiotic treatment, cf. alsoASAIO Journal 1992, p.M174-M178, Khoury et.al, “Prevention and Controlof Bacterial Infections Associated with Medical Devices”, andAntimicrobial Agents and Chemotherapy, Vol.38, No. 12, December 1994,p.2803-2809, Costerton et.al., “Mechanism of Electrical Enhancement ofEfficacy of Antibiotics in Killing Biofilm Bacteria” In these studies,generally, a low electric current of the order of 15-400 μA/cm² isapplied onto the infected surface while they were immersed in a bufferwith antibiotics. In the most successful studies a total killing ofmicroorganisms was reported after only 8 hours of current and antibiotictreatment—tobramycin 2.5 mg/l, 15-400 μA/cm², during 8 h. This effecthas been termed “the bioelectric effect”.

[0004] These studies suggest that the electric field need to be appliedin close proximity to the infected implant. A passive electric fieldwill not due, but a current should be conducted between electrodes inthe biofluid surrounding the implanted device. A possible explanation tothe observed effect is that electrochemically generated products areneeded for the bioelectric effect to occur. At the titanium surface,titanium being normally used in heart stimulator housings, the followingelectrochemical processes take place.

[0005] At the anode:

2 H₂O_(→)O₂+4 H⁺+4 e⁻  1)

2 Cl⁻ _(→)Cl₂+2 e⁻  2)

Ti+2 H₂O_(→)TiO₂+4 H⁺+4 e⁻  3)

[0006] At the cathode:

O₂+2 H₂O+4 e⁻ _(→)4 OH⁻  1)

2 H₂O+2 e⁻ _(→)H₂+2 OH⁻  2)

[0007] It is supposed that primarily the produced oxygen and chloridegases have an influence on the biofilm attached to the surface. It isalso supposed that the fact that the pH-value is lowered at the anodeand increased at the cathode is significant for the influence andviability of the biofilm.

[0008] An infection that is initiated in the stimulator pocket will alsooften start to spread along the lead. The polymer surface of the leadmay be a substrate for the bacteria and makes it easy for the bacteriato attach. At the time when a pocket infection is clinically manifested,in many cases the infection has already spread some distance from thestimulator pocket along the lead.

[0009] As the bioelectric effect is concentrated to parts in conjunctionwith or in close proximity to conducting surfaces of the implant, it isthe purpose of the present invention to extend these conducting activesurfaces to practically the whole exterior surface of the implant, suchthat it can be current covered.

DISCLOSURE OF THE INVENTION

[0010] This purpose is obtained by an apparatus of the type defined inthe introductory portion of the description and having thecharacterising features of claim 1.

[0011] As discussed above the bioelectric effect is limited toconducting surfaces of the implanted device or to the immediateproximity thereof. With the present invention a design is obtained whichmakes it possible to extend the bioelectric effect to traditionally nonconducting surfaces of an implanted heart stimulator, like a pacemakeror a cardioverter-defibrillator (ICD). By making also exterior surfacesof the proximal part of the lead and a possible connector topelectrically conductive all exterior stimulator surfaces located withinthe subcutaneous implant pocket and a part of the lead extending fromthe pocket are electrically conductive, and by adapting theseelectrically conductive surfaces to form at least two separateelectrodes and providing a current source to supply an electricinfection control current between these electrodes all exterior surfaceswill be current coated, and the bioelectric effect will be extended toall surfaces within the pocket and also to the exterior surface of theproximal part of the lead. By making the normally non-conductingsurfaces of the connector top and the lead electrically conducting notonly effective treatment of infections within the pocket is possible,but spreading of the infection from the pocket along the lead isprevented. The lead will in this way benefit from the bioelectric effectand thus it is prevented that bacteria reach the endocardium giving riseto endocarditis.

[0012] According to an advantageous embodiment of the apparatusaccording to the invention an electrically conducting polymer is appliedon said exterior surfaces of the proximal part of said lead and saidpossible connector top. In this way traditionally non-conductingsurfaces of a heart stimulator are made electrically conductive. Anexample of a polymer suitable for this purpose is an electricallyconducting polymer marketed under the trademark ELASTOSIL.

[0013] According to another advantageous embodiment of the apparatusaccording to the invention an electrically conducting coil is appliedaround said proximal part of the lead. In this way the proximal part ofthe lead is made not only electrically conductive but the wearresistance of the lead is improved.

[0014] According to still another advantageous embodiment of theapparatus according to the invention the exterior surfaces of theproximal part of the lead and of said possible connector top are treatedby ion implantation technology or so-calledIon-Beam-Assisted-Deposition. This technique is especially well suitedfor making stimulator connector tops or headers of epoxy electricallyconductive. Other possible coating technologies are Physical VapourDeposition, PVD, or Chemical Vapour Deposition, CVD, or any sputteringprocess.

[0015] It has been found that oxide layers, especially titanium oxidelayers but also other metal oxide layers, may be found when such metalsare used in the DC current environment dealt with in conjunction withthe present invention. These oxide layers may cause an uneven currentdistribution which is detrimental to the infection control effect. Thecurrent may also be lowered due to increased impedance because of theoxide layer to a point at which the effect on bacteria in the biofilm isno longer effective. The formation of such oxide layers is avoided,according to an advantageous embodiment of the apparatus according tothe invention, by coating the generator housing, and other metallicsurfaces that may become oxidised due to the DC current, with one of themetals platinum, palladium or iridium or any other metal with similarelectrochemical characteristics or an alloy of these metals

[0016] According to still other advantageous embodiments of theapparatus according to the invention said counter electrode is animplantable electrode, suitably designed to be positioned on said leadfor implantation into the patient's heart, preferably a heartstimulation electrode is forming said counter electrode. The need of aseparate implanted counter electrode is then eliminated. In this casethe electrical infection treatment has to be performed such that it doesnot interfere with stimulation pulses of the heart stimulator. Thus thetreatment has to be restricted to the heart's refractory periods, or,alternatively, an infection treatment current of such a high frequencyis used that the heart is not affected.

[0017] According to yet other advantageous embodiments of the apparatusaccording to the invention said counter electrode is formed of a largesurface defibrillation electrode, said counter electrode can be designedfor external application to the patient's skin, preferably formed of apatch electrode for external application to the patient's skin. By usinglarge surface electrodes the current density will be lower and a uniformcurrent distribution is more easily obtained.

[0018] When using an external current source, which is naturalparticularly in case of a counter electrode for external application, agalvanic connecting means is provided to galvanically connect to saidcurrent source to implanted electrodes through the patient's skinaccording to an advantageous embodiment of the apparatus according tothe invention.

[0019] According to other advantageous embodiments of the apparatus,according to the invention means are provided to inductively couple saidexternally located current source to said electrodes.

[0020] According to other advantageous embodiments of the apparatusaccording to the invention the inductive coupling means comprise a thininductive coil attached to the outer surface of the pulse generatorhousing and electrically connected to the electrodes or an inductivecoil positioned inside the pulse generator housing and electricallyconnected to the electrodes. Such thin coils, which are manufacturedpreferably by screen printing, will not require much space and willconsequently contribute to a compact stimulator construction. Such acoil might also be used as a telemetry coil.

[0021] According to still another advantageous embodiment of theapparatus according to the invention a rectifying means is connectedbetween said coil and one of the electrodes to supply a DC current tothe electrodes.

[0022] According to other advantageous embodiments of the apparatusaccording to the invention with said current source located externallyan electrolytic connecting means is provided for electrolyticallyconnecting said current source to said first electrode. Saidelectrolytic connecting means preferably comprises an additionalelectrode for external application to the patient's skin, separated fromsaid counter electrode and in electrolytic contact with said firstelectrode, said current source being connected to said counter electrodeand to said additional electrode. The biofluid of the patient's body canthen serve as electrolytic medium. In this way the great advantage of anon-invasive connection without transcutaneous wires is obtained. Whenusing two external (patch) electrodes the current distribution on thehousing and implanted electrode respectively might be non-uniform. Thiscan be, at least partly, remedied by repositioning the externalelectrodes during the treatment, such that all implanted surfaces arecoated by an adequate quantity of current.

[0023] The present invention also relates to a heart stimulatorcomprising a pulse generator for delivering electric stimulation pulsesto a patient's heart through a lead, connectable to said pulsegenerator, possibly through a connector top on a pulse generatorhousing, said pulse generator housing be electrically conductive, whichstimulator is characterised by an apparatus as disclosed above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] To explain the invention in greater detail embodiments of theapparatus according to the invention will now be described withreference to the drawings, on which

[0025]FIG. 1 shows schematically a heart stimulator with a lead providedwith a coil on its proximal part,

[0026]FIG. 2 shows an embodiment with a large surface ventriculardefibrillating electrode as counter electrode,

[0027]FIG. 3 shows schematically a heart stimulator with a surfacemounted coil on the exterior of the stimulator housing for inductivelyconnecting an external current source to the electrode forming parts ofthe implant, and

[0028]FIG. 4 shows an embodiment of the invention with an external patchelectrode as counter electrode.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0029] In the apparatus according to the invention a. o. the proximalpart of the lead extending to a position which after implantation of thelead is situated between a location beyond the entry into the venoussystem and the entry into vena cava superior, is made electricallyconductive. This can be realised in several different ways. Thus theproximal part can be made electrically conductive by e.g. applying anelectrically conducting polymer on its surface or by ion implantationtechnology or Ion-Beam-Assisted-Deposition (IBAD). In FIG. 1 anotherexample of making a proximal lead part electrically conductive is shown.

[0030] Thus FIG. 1 shows schematically an implantable heart stimulator 2having a connector top 4 to which a lead 6 is connected. The proximalpart of the lead 6 is made electrically conductive by wrapping ametallic coil 8 around this part of the lead. The metallic coil 8 willalso improve the wear resistance of the lead 6.

[0031] The connector top or header 4 is often made of epoxy and IBAD isa suitable technique for making such a connector top conductive

[0032]FIG. 2 shows an embodiment with electrically conductive exteriorsurfaces of the generator housing 10, the connector top 12 and theproximal part 16 of the lead 14. The generator housing 10, the connectortop 12 and the proximal part 16 of the lead 14 are forming oneelectrode, whereas a large surface right ventricular defibrillatingelectrode 19 on the lead 14 is used as counter electrode. The pulsegenerator battery can be operable to deliver an infection controlelectric current i between this defibrillation electrode 19 and theelectrode formed by the conductive housing 10, the connector top 12 andthe proximal lead part 16 to destroy bacteria residing in a biofilm onthe implanted stimulator. This electrical treatment current i must notinterfere with the stimulating function of the heart stimulator and istherefore delivered during the heart's 21 refractory period.

[0033] Other examples of implantable indifferent electrodes aredisclosed in e.g. U.S. Pat. Nos. 5,510,766 and U.S. Pat. No. 5,814,076,these electrodes, however, being used for other purposes.

[0034] The electric infection control requires a comparatively highamount of energy and therefore an external power source is normallyneeded. Transcutaneous electric connections to implanted electrodesincrease the risk of recontamination of the wound and discomfort for thepatient. It would therefore be a great advantage to use a non-invasivemethod for the energy supply.

[0035]FIG. 3 shows an example of supplying electric current forinfection control from an external source by electromagnetic induction.Thus a super thin surface mounted coil 18 is attached to the exteriorsurface of the stimulator housing 20. This coil 18 can be manufacturedby e.g. screen printing. A polymeric isolation film 22 is provided toelectrically isolate the coil 18 from the stimulator housing 20.

[0036] One end 24 of the coil 18 is electrically connected to thehousing 20, while the other end is connected to a diode 26 integrated inthe epoxy connector head 28. The diode 26, in its turn, is connected toa counter electrode 31.

[0037] By applying a high frequency electromagnetic field by an externalenergy source located in the proximity of the stimulator, a current willbe generated in the coil 18. The diode 26 will allow current in only onedirection for permitting the electrochemical processes necessary for thebioelectric effect to occur.

[0038] As an alternative, the coil can be implemented inside thestimulator housing. One end of the coil is then connected to thestimulator housing, whereas the other end of the coil is connected via adiode to an external counter electrode.

[0039]FIG. 4 shows an embodiment with the pulse generator housing 10,the connector top 112 and the proximal part 116 of the lead 114 formingone electrode, whereas an external patch electrode 122, intended forapplication on the patient's skin, Is used as counter electrode. In thiscase an external current source 124 is used for delivering treatmentcurrent i. When therapy had to be applied in this case, an electricallyconductive needle 126, connected to the current source 124, is insertedthrough the patient's skin to make contact with a pulse generatorhousing 10. This embodiment has the advantage that only minormodifications of existing hardware are needed, viz. making connector top112 and outer surface of the proximal lead part 116 electricallyconducting.

[0040] Numerous variations and modifications of the above describedembodiments of galvanically connection as shown in FIG. 4 and inductivecoupling of an externally located current source to implanted electrodesas exemplified in FIG. 3 are of course possible. As another alternativea connecting means can be used for electrolytically connecting anexternal current source to an implanted electrode. The electrolyticconnecting means can comprise an additional electrode for externalapplication to the patient's skin, separated from the counter electrodeand in electrolytic contact with said first electrode via the bodybiofluid. By connecting the current source to the counter electrode andto this additional electrode a non-invasive method of connecting thecurrent source is obtained.

[0041] When using external electrodes these electrodes should preferablybe positioned such that those parts of the infection control current,which pass through the heart, are minimised.

1. An infection control apparatus for an implantable heart stimulatorcomprising a pulse generator for delivering electric stimulation pulsesto a patient's heart (21) through a lead (6, 14, 114) connectable tosaid pulse generator, possibly through a connector top (4, 12,28, 112)on a pulse generator housing (2, 10,20, 110), said pulse generatorhousing being electrically conductive, characterized in that theexterior surfaces of said possible connector top (4, 12,28, 112) and ofa proximal part (8, 16, 116) of the lead (6, 14, 114) are electricallyconductive, said proximal part extending to a position which afterimplantation of the lead is situated between a location beyond the entryinto the venous system and the entry into vena cava superior, saidgenerator housing (2, 10, 20, 110) and said electrically conductivesurfaces of said proximal lead part and of said possible connector topbeing adapted to form a first electrode, and in that at least one secondcounter electrode (19, 31, 122) is adapted to be located outside thesubcutaneous pulse generator pocket in which the pulse generator islocated after implantation, a current source being provided to supply anelectric infection control current between said electrodes.
 2. Theapparatus according to claim 1, characterized in that an electricallyconducting polymer is applied on said exterior surfaces of the proximalpart (16, 116) of said lead (14, 114) and of said possible connector top(4, 12,28, 112).
 3. The apparatus according to claim 1, characterized inthat an electrically conducting coil (8) is applied around said proximalpart of said lead (6).
 4. The apparatus according to claim 1,characterized in that said exterior surfaces of the proximal (16, 116)of said lead (14, 114) and of said possible connector top (4, 12,28,112) are treated by ion implantation technology or so-calledIon-Beam-Assisted-Deposition or Physical Vapour Deposition, or ChemicalVapour Deposition, or any other sputtering process.
 5. The apparatusaccording to any one of the preceding claims, characterized in that saidgenerator housing (2, 10,20, 110) is coated with one of the metalsplatinum, palladium or iridium or any other metal with similarelectrochemical characteristics, or an alloy of these metals.
 6. Theapparatus according to any one of the preceding claims, characterized inthat said counter electrode (19) is an implantable electrode.
 7. Theapparatus according to claim 6, characterized in that said counterelectrode is designed to be positioned on said lead (14) forimplantation into the patient's heart (21).
 8. The apparatus accordingto claim 6 or 7, characterized In that a heart stimulation electrode isforming said counter electrode.
 9. The apparatus according to any one ofthe claims 1-6, characterized in that said counter electrode is formedof a large surface defibrillation electrode.
 10. The apparatus accordingto any one of the claims 1-9, said current source being externallylocated, characterized in that means (18) are provided to inductivelycouple said externally located current source to said electrodes. 11.The apparatus according to claim 10, characterized in that saidinductive coupling means comprise a thin inductive coil (18) attached tothe pulse generator housing (20) and electrically connected to theelectrodes.
 12. The apparatus according to claim 11, characterized inthat a rectifying means (26) is connected between said coil (18) and oneof the electrodes. 13 The apparatus according to any one of the claims1-5, characterized in that said counter electrode is designed forexternal application to the patient's skin.
 14. The apparatus accordingto claim 13, characterized in that said counter electrode is formed of apatch electrode (122) for external application to the patient's skin.15. The apparatus according to claims 13 or 14, said current source(124) being externally located, characterized in that a galvanicconnecting means (126) is provided to galvanically connect said currentsource (124) to implanted electrodes through the patient's skin.
 16. Theapparatus according to claims 13 or 14, said current source beingexternally located, characterized in that an electrolytic connectingmeans is provided for electrolytically connecting said current source tosaid first electrode through the patient's skin.
 17. The apparatusaccording to claim 16, characterized in that said electrolyticconnecting means comprises an additional electrode for externalapplication to the patient's skin, separated from said counter electrodeand in electrolytic contact with said first electrode, said currentsource being connected to said counter electrode and to said additionalelectrode.
 18. The apparatus according to any one of the claims 1-9,characterized in that said current source is formed of an electric pulsegenerator battery.
 19. A heart stimulator comprising a pulse generatorfor delivering electric stimulation pulses to a patient's heart (21)through a lead (6, 14, 114) connectable to said pulse generator,possibly through a connector top (4, 12,28, 112) on a pulse generatorhousing (2, 10,20, 110), said pulse generator housing being electricallyconductive, characterized by an apparatus according to any one of thepreceding claims.